Recently, we have noticed a problem with 3CXPhones. If an external caller calls in and the call is answered via 3CXPhone, the call cannot be put on hold or transferred. When the buttons on the 3CXPhone are pressed, it looks like they aren't doing anything at all, except that they do cause the call to be interrupted: you can't talk to the caller anymore, even though the call stays "active". The caller just basically gets dead air, doesn't hear anything happening anymore. All 3CXPhones seem to show this behavior, as best as I can tell. Outgoing calls do not show this behavior (if the 3CXPhone was used to make a call, the call can be put on Hold or Transferred just fine). If the call is answered with a desk phone, Hold and Transfer functions work just fine. If the call is answered with 3CXPhone, if the Presence screen is opened, you can right-click on the call there and Transfer or Park it just fine. Re-provisioning and re-installing the softphone do not seem to fix the problem. It's just the buttons on the 3CXPhone itself, and only for external incoming calls. When I looked into it deeper, the logs on the phone show that the phone does send a "put call on hold" command to the server (I think) and it looks like the server receives it (I can see an equivalent entry in the Server Activity Log), but there's this error message in the log: [22.01.2015 11:55:41.611] 11:55:41.611 PjsuaCallbacks .....Error: hold transaction successful but state is still HOLDREQUESTED which sounds like exactly what's happening. The call is being half put on hold but not fully, for some reason. Like maybe some "acknowledgement" isn't being received or something. Can anyone point me to any clues as to what's happening here? Why on earth could it be happening only for incoming outside phone calls?